Dry shaving apparatus

ABSTRACT

A dry shaving apparatus having an upper cutter with a rotary cutter carrier and a plurality of hook-shaped lower cutters supported by the carrier and cooperating with the upper cutter. The carrier has a straight guide for each of the lower cutters and each guide and lower cutter being disposed and proportioned so that the longitudinal direction of each guide describing an angle governed by the point of contact of the lower cutter edge with the upper cutter.

PATENTEDJAH 16 I975 SHEET 1 BF 2 FIG. I

.m zvm ATTORNEYS PATENTEDJAH 16 I973 sum 2 BF 2 INVENTOR ehzZel Mcj cfk w/H W ATTORNEYS The invention relates to dry shaving apparatus comprising an upper cutter, a rotary cutter carrier, and a plurality of hook-shaped lower cutters supported by the carrier and cooperating with the upper cutter, the carrier including a straight guide for each of the lower cutters, and each of the lower cutters consisting of two parts, namely a first part carrying a cutting edge cooperating with the upper cutter and a second part movable in the respective guide.

It is known that in dry shaving apparatus, which have rotarily driven lower cutters cooperating with an upper cutter, it is very generally of decisive significance, for achieving a good shaving efficiency, that the cutting edges of the lower cutters have undisturbed contact with the upper cutter which provides the cooperating cutting edges, and slide without play on the upper cutter. This must in particular be ensured even during the shaving operation, i.e. during the cutting of the hairs and the operation of the consequent cutting forces. Any lifting of the cutting edges of the lower cutters from the upper cutter would cause the shave to become defective and painful, because it would lead to the known effect of tearing.. Hitherto it has therefore been usual to enforce a smooth engagement of the edges of the lower cutters on the upper cutter, either by a correspondingly large spring force or through employment of centrifugal force. But the larger these pressing forces are, the larger is the friction between the lower cutters and the upper cutter, and consequently an undesired heating occurs and a relatively large driving power is necessary. These undesired effects also occur during idle running of the apparatus.

The invention has aimed at avoiding these difficulties in a particularly simple manner. A dry shaving apparatus constructed according to the invention, of the kind stated above, has each guide and lower cutter so disposed and proportioned that the longitudinal direction of each guide makes, with the tangent drawn at the instantaneous point of contact of the lower cutter edge with the upper cutter to the path swept out by the cutting edge along the upper cutter, an angle, enclosing the cutting edge, of between and 65, whereby the pressing of each lower cutter on the upper cutter during shaving chiefly occurs through a component of the cutting forces which arise during cutting of the hairs.

At the basis of the invention lies the recognition that the cutting forces which arise of themselves during shaving, by the cutting of the hairs, can be used to press the hook-shaped lower cutters against the upper cutter during the shaving process. By this means a close engagement of the lower cutter edges on the upper cutter, and thus an undisturbed cutting action, are obtained during shaving. During idle running of the apparatus, on the contrary, these pressing forces cease, so that the friction is minimal.

A particularly good use of the cutting forces to press the lower cutter edges on the upper cutter is obtained if the ratio of the length of the portionof each second part engaged by the respective guide,to the length of the portion of the second partextending beyond the guide in the longitudinal direction of the latter and reckoned as far as the projection of the cutting edge onto this longitudinal direction, lies in the range between 0.5 and 5.

Advantageously, springs with slight force, preferably in the order of magnitude of 10 pond (l0 gram-weight) act between the carrier and the lower cutters and serve for engaging the lower cutters lightly against the upper cutter in the rest condition or during idle running of the apparatus, so that the lower cutters are held continuously in gentle contact with the upper cutter, and thus are always ready for operation. The forces exerted in this way lie far below those which are necessary to provide the necessary pressing force for the lower cutters on the upper cutter during cutting of the hairs, so that the friction produced thereby can practically be neglected.

The invention will be described in more detail below with reference to the accompanying drawings, in which some constructional examples are shown, to which however the invention is not restricted. In these' drawings:

FIG. 1 shows in cross section along the line I --l in FIG. 2; and

FIG. 2 in plan and partly in section, the part relevant to the invention of a first example, in which the lower cutters cooperate with a circular fixed perforated cutter as upper cutter,

FIG. 3 is a schematic sketch which serves to illustrate the general inventive concept,

FIG. 4 shows in cross section the part relevant to the invention of asecond example, in which the lower cutters cooperate with an upper cutter formed as a lightly bowed cutter foil; in connection with this example,

FIG. 5 shows the cutter carrier in plan,

FIG. 6 shows a lower cutter in perspective, and I FIG. 7 shows in cross section a detail of the bearing of a lower cutter in the cutter carrier,

FIG. 8 shows a variant for the construction of the lower cutters,

In FIG. 9 a third example is shown schematically, in which the lower cutters cooperate with an upper cutter formed as a cutter foil extending in a bowed shape.

In FIG. 1 the housing of a dry shaving apparatus is indicated at l, on which an upper cutter 3 is fixed by means of a ring 2. This upper cutter is made circular and has on its upper side 4 hair entry openings 5 to form a perforated cutter. With this upper cutter there cooperate lower cutters 6, which are arranged movably in a disc-shaped cutter carrier 7. The cutter carrier fits on a shaft 8, which is driven in the direction of the arrow 9 by a motor of the apparatus, which is not shown further.

As can be seen from the drawing, four lower cutters 6 are provided, each displaced at from one another.

Each lower cutter is formed hook-shaped,'and a first I part 10 carries a cutting edge 11 at its free end, while a second part 12, at an angle to this first part, serves for mounting the lower cutter in the cutter carrier 7. The

,cutter carrier 7 has for this purpose for each lower cutter a slit 13, the side walls of whichform a straight guide for each lower cutter and thus guide the parts 12 Now, according to the invention, the longitudinal direction 17 of each guide 13 makes, with the tangent l8 drawn at the instantaneous point of contact of the lower cutter edge with the upper cutter to the path of the cutting edge 11 along the upper cutter 3, an angled), enclosing the cutting edge, which lies between 10 and 65. This has the consequence that the pressing of the hook-shaped lower cutters against the perforated cutter foil during shaving is the result principally of the cutting forces which occur during cutting of the hairs. That is to say, if a hair extends through a hair entry opening 5, and a cutting edge 11 comes into engagement with this hair, then during cutting of the hair, a cutting force arises in the direction of the arrow 19, which has a component of force in the longitudinal direction 17 of the guide 13. This component of force acting on the lower cutter has the tendency to pull the lower cutter out of the guide and press it against the upper cutter. In this manner the pressing forces for the lower cutters on the upper cutter are produced automatically by the cutting forces which arise during shaving. The greater the cutting forces are, that is to say the more hair or the thicker hair that is cut, to the same extent the pressing forces are greater, which press the lower cutters with their cutting edges against the upper cutter, i.e. the more strongly are the lower cutters pulled out of the guides. Thus this measure ensures that the cutting forces themselves, which in known constructions of this kind frequently produce an undesired effect, namely a lifting of the lower cutters from the upper cutters which must then be again overcome by additional spring forces which produce friction is now employed effectively for the purpose of applying the lower cutters fully against the upper cutter, during the shaving operation, so that a good quality of shaving is achieved. In the known devices, upon increase in the cutting forces, there is an increase in the danger of the lifting of the lower cutters from the upper cutter; by the measures according to the invention such a danger does not exist at all, because in such a circumstance the lower cutters, by reason of the greater cutting forces, are pressed more strongly against the upper cutter and thus absolutely certainly remain in contact with the latter.

During idle running of the apparatus, when no hairs are being cut, the cutting forces cease, so that the lower cutters are no more pressed by cutting forces against the upper cutter, so that the resultant friction between the lower cutters and the upper cutter ceases and an undesired heating is avoided. In order to maintain the lower cutters always in contact with the upper cutter 3 during such an idle running time or in the rest condition of the apparatus, and thus hold the cutters ready for cutting, the springs 16 already referred to are provided. These springs 16 have however only slight force, preferably in the order of magnitude of 10 pond (l0 gram-weight), so that the pressing forces produced by them are so slight that the friction arising from these pressing forces between the lower cutters and the upper cutter is practically negligible.

With reference to FIG. 3, the inventive concept will be further explained. Here there is shown schematically a curved upper cutter 3, with which cooperates a hookshaped lower cutter 6. The upper cutter is to be considered as a surface of rotation, while the lower cutter rotates about the axis of rotation. The hook part 12 of the lower cutter is movable in the longitudinal direction 17 in a straight guide, which here consists of two bearings 20, in a cutter carrier which is not shown in more detail. The tangent to the path of the cutting edge 1 1 along the upper cutter is further shown at 18. Of importance is the angle 4:, enclosing the cutter edge, between the longitudinal direction 17 and the tangent 18, which according to the invention should lie in the range between 10 and 65, because otherwise the lower cutter will extend so steeply or so flatly in relation to the upper cutter, that the pressing effect according to the invention will no longer be achieved. If the lower cutter 6 progresses in the direction of the arrow 9, then upon cutting of hairs a cutting force arises in the direction of the arrow 19, which has a force component 21 in the longitudinal direction 17 of the guide, which, as already explained, tends to press the lower cutter 6 with its cutting edge 11 against the upper cutter 3.

Perpendicular to the force component 21 there also works a force component 22, which presses the lower cutter against the guide. This force component must naturally in no case have the effect that the movability of the lower cutter in the guide is impaired.

It has been found to be particularly advantageous, if the ratio of the length of the portion of the hook part 12 engaged by the guide, to the length of the portion of this part extending beyond the guide in the longitudinal direction of the latter and reckoned as far as the projection of the cutting edge onto this longitudinal direction, lies in the range between 0.5 and 5. In FIG. 3 the portion of the hook part 12 engaged by the guide is marked a; in general under this heading should be understood that portion which corresponds to the two outermost ends of the entire straight guide, regardless of how many guiding places this has. The portion which extends beyond the guide 20 in the longitudinal direction 17 of the latter as far as the projection of the cutting edge 11 upon this longitudinal direction is marked b in FIG. 3. By the choice given above of the ratio of a to b, the result is achieved that the cutting forces arising during shaving will apply the lower cutter especially effectively against the upper cutter, with unimpaired movability in the guide.

In the example according to FIG. 4 a perforated cutter foil is used as the upper cutter 3', which is tensioned with its edge in a ring 23, which can be screwed onto the housing 1" of the apparatus. With its central part, this perforated cutter foil engages on the free end of an axle 24 fixed in the apparatus, on which a cutter carrier 7' for the lower cutters 6' is freely rotatably arranged. For drive of the cutter carrier, the latter is connected with a toothed wheel 25, which cooperates with another toothed wheel 26, which is connected to a motor not further shown.

The cutter carrier 7 shown in plan in FIG. 5 has two groups of slits, 27 and 28 respectively, offset radially from one another, in which the hook-shaped lower cutters 6, shown in FIG. 6, can be inserted. The two groups of slits are in this connection so arranged that the paths of both cutter groups overlap, so that the individual lower cutters can be made narrower, while nevertheless a large area of the upper cutter can be uniformly covered by them.

As can be seen from FIG. 7, the slits 27, 28 are arranged at an angle (15, which lies between 10 and 65,

while the lower cutters are guided corresponding to the length of the portion a and extend beyond the guide by an amount corresponding to the length of the portion b. It has been found particularly advantageous in this connection if the angle (1) is chosen at 45 and the ratio of a b at 3. A central bore 29 in the slits serves to receive a weak spring 16, which abuts on the one hand against the end of the bore and on the other hand against the end faces 30 of two recesses 31 formed in the lower cutter 6. These springs urge engagement of the lower cutters on the perforated cutter foil, so that the lower cutters are always ready for operation. If desired, means can also be provided, by which the lower cutters cannot be expelled from the slits unintentionally, when the perforated cutter foil is removed from the apparatus.

The mode of operation of this apparatus is analogous to that already described above, that is to say again the lower cutters, under the action of the cutting forces which arise on cutting of the hairs, are pressed completely against the perforated cutter foil.

FIG. 8 shows another constructional form of a lower cutter 6' for such an apparatus, in which the hook form is simply obtained, in that, in order to form the cutting edge 1 1', a hollow groove 32 is ground in a cutter plate In the example according to FIG. 9 there is provided as upper cutter 3 a perforated cutter .foil which is cylindrically curved and engaged in the neighborhood of its longitudinal edges on parts of the apparatus 1". The hook-shaped lower cutter 6" are here arranged along the circumference of a drum-shaped cutter carrier 7", which is rotatably supported in the apparatus and driven by a motor. Obliquely extending slits 34 are provided in the cutter carrier, which serve as guides for the respective parts 12" of the lower cutters, while the longitudinal directions 17" of the latter enclose theangle d) with the tangent 18" at the point of contact of the cutting edge 11" of the lower cutter with the perforated cutter foil. 1

In this example no springs are provided for bringing the lower cutters against the perforated cutter foil, but this action occurs by the centrifugal force acting on the lower cutters when the cutter carrier is rotating. The mass of each lower cutter is so chosen in this connection that, at the nominal speed of rotation of the cutter carrier, only a light engagement of the lower cutters on the upper cutter occurs, so that the centrifugal forces arising only bring the lower cutters into the position in which they can just begin a cutting action, that is to say, they are ready for operation. To limit the possible movability of the lower cutters in the slits 34, slits 35 are provided in their hook parts 12", into which pins 36 extend, which are inserted in the cutter carrier 7".

The pressure of the lower cutters on the perforated cutter foil necessary for satisfactory cutting of the hairs occurs again through the cutting forces which arise during shaving, which pull the lower cutters outwards in the guides and engage them fully against the perforated cutter foil.

Naturally a quantity of modifications of the examples described are possible, without going outside the scope of the invention. In this connection reference will particularly be made to the kind and type of construction of the hook-shaped lower cutters and their guides in the cutter carrier, and also to the universal employability of the measures according to the invention in the various systems of dry shaving apparatus with rotary hookshaped cutters.

I claim:

1. In a dry shaving apparatus including an upper cutter, a rotary cutter carrier, and means for rotating said carrier, the improvement in combination therewith comprising a plurality of hook-shaped lower cutters supported by the carrier and cooperating with the upper cutter, the carrier having a straight guide for each of the lower cutters, and each of the lower cutters having a first part carrying a cutting edge cooperating with the upper cutter and a second part movable in one of said guides, each of said guides: restricting the lower cutter movement to substantially linear movement, each guide and lower cutter being so disposed and proportioned that the longitudinal axis of each guide makes an angle of between 10 and 65 with the tangent drawn to the upper cutter at the instantaneous point of contact of the lower cutter cutting edge with the upper cutter on the path swept by the cutting edge along the upper cutter, whereby each lower cutter is urged against the upper cutter during shaving chiefly through a component of the cutting forces which arises during cutting of the hairs.

2. A dry shaving apparatus according to claim 1, wherein there is a ratio in the range of 0.5 to 5 of the length of the portion of each second part engaged by the respective guide, to the length of the portion of the second part extending beyond the guide in the longitudinal direction of the latter extending to the projection of the cutting edge onto this longitudinal direction.

3. A dry shaving apparatus according to claim 1 further comprising springs with slight force, each of which acts between the carrier and a lower cutter and serves for urging the lower cutter slightly against the upper cutter in the rest condition and during idle running of the apparatus.

4. In a dry shaving apparatus including an upper cutter, a rotary cutter carrier, and means for rotating said carrier, the improvement in combination therewith comprising a plurality of hook-shaped lower cutters supported by the carrier and cooperating with the upper cutter, the carrier having a straight guide for each of the lower cutters, and each of the lower cutters having a first part carrying a cutting edge cooperating with the upper cutter and a second part movable in one of said guides, each guide and lower cutter being disposed and proportioned such that the longitudinal axis of each guide makes an angle of between 10 and 65 with a tangent drawn to the upper cutter at the contact point thereon by said lower cutter cutting edge, whereby each lower cutter is urged against the upper cutter during shaving chiefly through a component of the cutting forces which arises during cutting hairs, the apparatus further comprising at least one spring acting between the carrier and each lower cutter and urging said lower cutter slightly against the upper cutter.

5. Apparatus according to claim 4 wherein said carrier has an axis of rotation, and each guide of the carrier has an axis non-parallel with said rotation axis, whereby a centrifugal force component is developed urging each lower cutter to move relative to said guide toward said upper cutter. 

1. In a dry shaving apparatus including an upper cutter, a rotary cutter carrier, and means for rotating said carrier, the improvement in combination therewith comprising a plurality of hook-shaped lower cutters supported by the carrier and cooperating with the upper cutter, the carrier having a straight guide for each of the lower cutters, and each of the lower cutters having a first part carrying a cutting edge cooperating with the upper cutter and a second part movable in one of said guides, each of said guides restricting the lower cutter movement to substantially linear movement, each guide and lower cutter being so disposed and proportioned that the longitudinal axis of each guide makes an angle of between 10* and 65* with the tangent drawn to the upper cutter at the instantaneous point of contact of the lower cutter cutting edge with the upper cutter on the path swept by the cutting edge along the upper cutter, whereby each lower cutter is urged against the upper cutter during shaving chiefly through a component of the cutting forces which arises during cutting of the hairs.
 2. A dry shaving apparatus according to claim 1, wherein there is a ratio in the range of 0.5 to 5 of the length of the portion of each second part engaged by the respective guide, to the length of the portion of the second part extending beyond the guide in the longitudiNal direction of the latter extending to the projection of the cutting edge onto this longitudinal direction.
 3. A dry shaving apparatus according to claim 1 further comprising springs with slight force, each of which acts between the carrier and a lower cutter and serves for urging the lower cutter slightly against the upper cutter in the rest condition and during idle running of the apparatus.
 4. In a dry shaving apparatus including an upper cutter, a rotary cutter carrier, and means for rotating said carrier, the improvement in combination therewith comprising a plurality of hook-shaped lower cutters supported by the carrier and cooperating with the upper cutter, the carrier having a straight guide for each of the lower cutters, and each of the lower cutters having a first part carrying a cutting edge cooperating with the upper cutter and a second part movable in one of said guides, each guide and lower cutter being disposed and proportioned such that the longitudinal axis of each guide makes an angle of between 10* and 65* with a tangent drawn to the upper cutter at the contact point thereon by said lower cutter cutting edge, whereby each lower cutter is urged against the upper cutter during shaving chiefly through a component of the cutting forces which arises during cutting hairs, the apparatus further comprising at least one spring acting between the carrier and each lower cutter and urging said lower cutter slightly against the upper cutter.
 5. Apparatus according to claim 4 wherein said carrier has an axis of rotation, and each guide of the carrier has an axis non-parallel with said rotation axis, whereby a centrifugal force component is developed urging each lower cutter to move relative to said guide toward said upper cutter. 